Anyone ever try "power scaling" in an amp?

Discussion in 'Amps and Cabs' started by clunk, Aug 22, 2005.

  1. clunk

    clunk Member

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    I was recently reading something about power scaling, a patent designed by Kevin O'Conner of London Power (www.londonpower.com). I could see something like that being usefull in Plexi type or single channel amps that generally derive there overdrive through the output tubes as apposed to preamp tubes. I talked to Kevin over the phone about this. it allows you to dial in the amount of wattage output preserving both tube life and speakers as apposed to using a power attenuator which does nothing to preserve tubes. Technically i have no idea how exactly this works though.
    Just wanted to know if anyone has tried this mod out on any amps at all and how it sounds? I know Stephenson Amps uses this patent in the manufacture of his amps but i have not yet heard one.
    BTW for those of you more technical minded folks, look up his books The Ultimate Tone, tons of very informative info about amp design and mods. I did get the first two books of that series. Slowly learning some stuff about amps, although a tech im deffinatly not. I only understand the theory of the way amps work with very limited technical knowledge. His books get right into details on resistors, caps, tranny's etc. and there layout with tons of possabilities. Its a good read.
    Anyway getting back to Power scaling. If any have tried the mod, how does it sound?

    Clunk
     
  2. Lerxst2112

    Lerxst2112 Member

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    Bit OT, but I ordered Principles of Power and The Ultimate Tone 1. Principles of Power should be here tomorrow... hope it's not TOO over my head.
     
  3. Lerxst2112

    Lerxst2112 Member

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    Actually, my fault, I ordered Principles of Power and Ready Set Go!
     
  4. clunk

    clunk Member

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    hehe. Some of it was a bit over my head. You really have to know schematics to really apprecitae the books value. Apperently the third book and up is where it really starts to get technical. Deffinatly over my head. All i can say is this guys a true engineer.

    Clunk
     
  5. SeanF

    SeanF Member

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    never tried Power Scaling, although I've known about it for years; I think I've got the kit around here somewhere. If I had to have the best master volume in the world, that's what I'd use, but I rarely have a need for master volume.

    just got TUT 5, man, what a wealth of info & designs.
     
  6. Lerxst2112

    Lerxst2112 Member

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    See, I don't understand schematics AT ALL. I look at one of those schematics for anything and I'm just completely and 100% baffled. Is there nothing that explains it?
     
  7. clunk

    clunk Member

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    Well Lerxst Im in a similar kinda boat. I can read schematics but im not knowledgeable about resistor values and how to read there colour codes. A good start to this i guess would be to find books on resistor values with pictures, then id have a clearer picture of what im looking at in an amp with reference to schematics.
    Aside from my original question on "has anyone tried power scaling?" Does anyone know any good reference books on resistor values?

    Clunk
     
  8. Lerxst2112

    Lerxst2112 Member

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    Well, can you point me towards something good on how to read schematics? I'm eager to learn...
     
  9. clunk

    clunk Member

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    Not really. Most of the schematics i learned some about were books from Devry Institute of electronics which were some books i found recently at my fathers house from his days of attending that college back in the 60's or 70's. They had books on resistors too but he hasnt been able to dig them up for me yet. Other than this i can't really say. Still looking though.

    Clunk
     
  10. clunk

    clunk Member

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    I shouldnt say CAN read. More like SOMEWHAT read. I'm more or less a beginner here.
    Anyway, anyone try power scaling?

    Clunk
     
  11. theelectic

    theelectic Guest

    You'll have to wait until TUT4 (to be released later this year I hope) if you want a full on, blow by blow of how power scaling works. It's hinted at in TUT2, and you get a schematic in TUT5. If you can put all the parts together, it's fairly simple to figure out.

    I've installed power scaling into a SF Champ and it works great (I have pics and other notes on my blog, which just happens to be down at the moment). In my Champ, PS takes down the wattage from 7 to 0.01W! OK you may be wondering why the heck do you have to install PS in an amp rated for 6W? 6W is still friggin' loud! Maybe not compared to a 100W Marshall, but crank it up and it's still too loud for late night playing. And the max PS setting (lowest power) the cranked tone is still there in spades. So are lots of other tonal shades not possible with the stock amp.

    I'll post links once I get everything up and running again.
     
  12. clunk

    clunk Member

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    Thanks for the info theelectric. Just wanted to know if it compromised the amps tone. I like the idea of using this more than an attenuator. Aside from a Two Rock amp most of my other amps are Fenders which is where i'd like to try this out and my Marshall. I just never heard tell of people using this mod much. Thanks again.

    Clunk
     
  13. loverocker

    loverocker Member

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    Power Scaling does what it does very well. I've got one of KOC's amps (the London Power Studio) which has PS and it works as advertised. I've also had a PSK kit for over a year, but never gotten around to fitting it into an amp :rolleyes: It is harder to fit in some amps (100W plexi) than others (Tweed Deluxe).

    For a basic guide to amp circuits (and a step-by-step) walkthough of the schematic of a simple Champ-like amp, have a look at the P1 theory guide at AX84 - http://195.178.239.50/ax84/media/ax84_m35.pdf

    The Torres book (Inside Tube Amps?) has a pretty good beginner's explanation, too.

    Here's a resistor colour code chart:
    [​IMG]
     
  14. darko

    darko Member

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    Check this site http://www.bruceclement.com/music/
    under PSK report, it is explained very well.
    Darko
     
  15. reeves amps

    reeves amps Member

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    I think it works great! If I thought for a moment that Power Scaling was flawed or negatively affected the tone I would have never put this technology in our new amplifiers.

    Bill
     
  16. RichSZ

    RichSZ Member

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    Yep...I heard the 50 watt Reeves amp first hand and the awesome thing about it when it was the amp was scaled down the tone was just as sweet at low volumes as it was when it was roaring.

    Power scaling is one of thoise things that lets you own a 50 or 100 watt amp and makes it useable in any situation.

    -Rich
     
  17. reachjkh

    reachjkh Member

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    Mojave? I thought I read about this while reading about the Coyote.
     
  18. drbob1

    drbob1 Silver Supporting Member

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    I've got a London Power Session amp with PS and with certain caveates it works well. The basic theory is that you separate the voltages that run the heaters (stay at 12v), the bias and the B+ (high voltage) power, so that you can adjust them individually. Then you can turn down the B+ without screwing up bias and reduce the amps total output. No way of doing this is going to completely leave the amp's tone alone for two reasons:
    1. The Fletcher-Munson curves tell us that the bass and treble are going to sound less distinct as you turn down. This is why your stereo has a loudness switch. This can be partly compensated for by pushing the bass and treble up as you turn down.
    2. The power curves aren't exactly the same as you reduce B+.

    The net result with my amp is that as I turn down the output the amp starts to sound a little cardboardy. I can compensate with EQ and by reducing the gain, plus Kevin has a new mod that helps, but extremes of reduction do change the sound. To me, the ideal way to reduce power is to combine Power Scaling, inefficient speakers and attenuators so that each contributes 6 dB or so, dropping your total output by 64 times...
     
  19. rooster

    rooster Member

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    I use it, kinda sorta. I use an 18W amp on stage, tweak the volumes of the channels to where I like them, put a mic in front of the speaker, and pump it through the PA to fill up the house and run through the monitors. Why would I want to make a 100W amp and run it at 20W? I'd rather take the small amp and make it run louder.

    I guess that sounds like a stupid approach, but it works for me.

    rooster.
     
  20. theelectic

    theelectic Guest

    Er, if your amp doesn't have Power Scaling installed, you don't actually use it. You're just micing your amp.

    As for running a 100W amp at 20W: easy, the tone of that 100W amp cranked up sounds killer, but it will also kill everyone in the audience or get you thrown out (or the cops called if you're at home). You also get greatly increased tube life. It's all explained here:

    http://www.londonpower.com/pscaling.htm
     

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